For those who aren't aware what are those major bugs and issues, here are some obvious system crises found in Android 4.3 firmware:
1. Wake up lag issues which takes a few seconds for the device to become active from standby.
2. Random system freezing that varies from time to time.
3. Massive battery drain without any possible quick fix.
4. Bluetooth Audio problems during playback inside your car.
5. Samsung music player suffers from stuttering audio playback.
6. Black screen that freezes the phone whenever a call is received.
7. RAM management goes poorer than Android 4.1.2.
8. Certain Wi-Fi connectivity issues.
http://au.ibtimes.com/articles/523237/2013...tm#.UsOrsvQW1MEi tried flashing the latest version (?) from china 1 if not wrong, but failed... current version is uk 4.3 rom i9300XXUGMK6

Bro.. outdated information already. All above solved after MK6 released. Now latest is ML2 that is much much more stable, good performance and battery. My phone drop 1% only of course without data and wifi.